U.S. patent application number 10/580722 was filed with the patent office on 2007-07-19 for method and apparatus for supporting downlink joint detection in tdd cdma systems.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS N.V.. Invention is credited to Yueheng Li, Li Sun, Gang Wu.
Application Number | 20070165620 10/580722 |
Document ID | / |
Family ID | 34624442 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070165620 |
Kind Code |
A1 |
Li; Yueheng ; et
al. |
July 19, 2007 |
Method and apparatus for supporting downlink joint detection in tdd
cdma systems
Abstract
A method is proposed for supporting downlink JD (joint
detection) in a TDD CDMA communication network system, comprising
steps of: judging whether the CAI (code allocation information) in
a downlink timeslot will change in the next TTI (transmission time
interval); if the CAI will change, inserting the changed CAI as a
specific control information into a specified field in the traffic
burst in the downlink timeslot corresponding to current TTI;
sending the traffic burst containing the specific control
information to each UE (user equipment) in the downlink timeslot
via a downlink channel.
Inventors: |
Li; Yueheng; (Shanghai,
CN) ; Sun; Li; (Shanghai, CN) ; Wu; Gang;
(Shanghai, CN) |
Correspondence
Address: |
PHILIPS ELECTRONICS NORTH AMERICA CORPORATION;INTELLECTUAL PROPERTY &
STANDARDS
1109 MCKAY DRIVE, M/S-41SJ
SAN JOSE
CA
95131
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS
N.V.
Eindhoven
NL
5621 BA
|
Family ID: |
34624442 |
Appl. No.: |
10/580722 |
Filed: |
November 4, 2004 |
PCT Filed: |
November 4, 2004 |
PCT NO: |
PCT/IB04/52293 |
371 Date: |
May 24, 2006 |
Current U.S.
Class: |
370/376 ;
370/458; 375/E1.025 |
Current CPC
Class: |
H04B 1/7105 20130101;
H04B 2201/709709 20130101 |
Class at
Publication: |
370/376 ;
370/458 |
International
Class: |
H04L 12/50 20060101
H04L012/50 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 27, 2003 |
CN |
200310118644.2 |
Claims
1. A method for supporting downlink JD (joint detection) in a TDD
CDMA communication network system, comprising: (a) judging whether
the CAI (code allocation information) in a downlink timeslot will
change in the next TTI (transmission time interval); (b) inserting
the changed CAI as a specific control information into a specified
field in the traffic burst in the downlink timeslot corresponding
to current TTI if the CAI will change; (c) sending the traffic
burst containing the specific control information to each UE (user
equipment) in the downlink timeslot via a downlink channel.
2. The method of claim 1, further comprising: when establishing
connection with a UE, the network system sends the initial CAI to
the UE.
3. The method of claim 2, wherein step (a) further includes: (a1)
judging that the CAI changes if at least one active UE leaves the
downlink timeslot; (a2) reclaiming the spreading code resource
released by the UE; wherein the changed CAI in step (b) is the CAI
after the spreading code resource is reclaimed.
4. The method of claim 2, wherein step (a) further includes: (a1)
judging that the CAI changes if at least one UE joins the downlink
timeslot; (a2) allocating spreading code resource to the UE;
wherein the changed CAI in step (b) is the CAI after the spreading
code resource is allocated.
5. The method of claim 2, wherein step (a) further includes: (a1)
judging that the CAI changes if the spreading code resource in the
downlink timeslot is reallocated to realize optimized configuration
of the resource in the downlink timeslot; wherein the changed CAI
in step (b) is the CAI after the spreading code resource is
reallocated.
6. The method in claim 1, wherein the specific control information
allows each UE in the downlink timeslot to perform one of the two
JD methods of ZF-BLE and MMSE-BLE.
7. A method for supporting downlink JD to be performed by a UE in a
TDD CDMA communication system, comprising steps of: (i) receiving a
traffic burst in a downlink timeslot transferred by the network
system via downlink channel; (ii) detecting whether the traffic
burst contains the CAI in the next TTI in the downlink timeslot;
(iii) extracting the CAI if the traffic burst contains the CAI;
(iv) performing next-phase JD algorithm to decrease interference by
using the CAI.
8. The method of claim 7, further comprising: the UE receives the
initial CAI from the network system when the UE establishes
connection with the network system.
9. The method of claim 8, wherein the JD algorithm is one of ZF-BLE
and MMSE-BLE.
10. A method for supporting downlink single-user JD in a TDD CDMA
communication network system, comprising steps of: (a) judging
whether the ACN (active code number) in a downlink timeslot will
change in the next TTI; (b) inserting the changed ACN as a specific
control information into a specified field in the traffic burst in
downlink timeslot corresponding to current TTI if the ACN will
change; (c) sending the traffic burst containing the specific
control information to each UE in the downlink timeslot via
downlink channel.
11. The method of claim 10, further comprising: the network system
sends the initial ACN to the UE when the network system establishes
connection with the UE.
12. The method of claim 11, wherein the specific control
information allows each UE in the downlink timeslot to perform an
MMSE-BLE-SD JD algorithm.
13. A method performed by a UE for supporting downlink single-user
JD in a TDD CDMA communication system, comprising steps of: (i)
receiving a traffic burst transferred by the network system via
downlink channel in a downlink timeslot; (ii) detecting whether the
traffic burst contains the ACN in the next TTI in the downlink
timeslot; (iii) extracting the ACN if the traffic burst contains
the ACN; (iv) performing the next-phase JD algorithm to decrease
interference by using the ACN.
14. The method of claim 13, wherein the step to be taken before
step (i) further includes: the UE receives the initial ACN from the
network system when the UE establishes connection with the network
system.
15. The method of claim 14, wherein the JD method is an MMSE-BLE-SD
method.
16. A network system for supporting downlink JD, comprising: a
judging unit, for judging whether the CAI in a downlink timeslot
will change in the next TTI; an inserting unit, for inserting the
changed CAI as a specific control information into a specified
field in the traffic burst in downlink timeslot corresponding to
current TTI when the CAI changes; a sending unit, for sending the
traffic burst containing the specific control information to each
UE in the downlink timeslot via a downlink channel.
17. The network system of claim 16, wherein the sending unit sends
the initial CAI to the UE when establishing connection with the
UE.
18. The network system of claim 16, wherein the judging unit judges
that the CAI changes if at least one active UE leaves the downlink
timeslot or at least one UE joins the downlink timeslot or the
spreading code resource in the downlink timeslot is
reallocated.
19. A UE for supporting downlink JD, comprising: a receiving unit,
for receiving a traffic burst transferred by the network system via
downlink channel in a downlink timeslot; a detecting unit, for
detecting whether the traffic burst contains the CAI in the next
TTI in the downlink timeslot; an extracting unit, for extracting
the CAI when the traffic burst contains the CAI; a performing unit,
for performing next-phase JD algorithm to decrease interference by
using the CAI.
20. The user equipment of claim 19, wherein the receiving unit
receives the initial CAI from the network system when establishing
connection with the network system.
21. A network system for supporting downlink single-user JD,
comprising: a judging unit, for judging whether the ACN in a
downlink timeslot will change in the next TTI; an inserting unit,
for inserting the changed ACN as a specific control information
into a specified field in the traffic burst in the downlink
timeslot corresponding to current TTI when the ACN changes; a
sending unit, for sending the traffic burst containing the specific
control information to each UE in the downlink timeslot via
downlink channel.
22. The network system of claim 21, wherein the sending unit sends
the initial ACN to the UE when establishing connection with the
UE.
23. A UE for supporting downlink single-user JD, comprising: a
receiving unit, for receiving a traffic burst transferred by the
network system via downlink channel in a downlink timeslot; a
detecting unit, for detecting whether the traffic burst contains
the ACN in the downlink timeslot in the next TTI; an extracting
unit, for extracting the ACN when the traffic burst contains the
ACN; a performing unit, for performing next-phase single-user JD
algorithm to decrease interference by using the ACN.
24. The UE of claim 23, wherein the receiving unit receives the
initial ACN from the network system.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to a communication
method and apparatus, and more particularly, to a method for
supporting downlink JD (joint detection) in TDD CDMA communication
systems, such as TD-SCDMA system.
BACKGROUND OF THE INVENTION
[0002] In TDD CDMA based wireless communication systems, there are
mainly two intra-cell interferences: one is MAI (multiple access
interference), caused by sharing of the same frequency band by
different users and the loss of orthogonality between the spreading
codes allocated for different users due to the multipath channel
effects; another is ISI (inter-symbol interference) between
different paths of the same user, caused by multipath
propagation.
[0003] To effectively mitigate MAI and ISI, JD (joint detection) is
introduced to conventional TDD CDMA communication systems. JD takes
full advantage of the spreading codes, channel fading, signal delay
and other information about the user signal, so it can improve
signal transmission quality in the cell and increase TDD wireless
communication system capacity. Furthermore, JD is suitable for
existing HCR (HCR: High Chip Rate, 3.84Mchip/s) and LCR (LCR: Low
Chip Rate, 1.28Mchip/s) TDD systems, and even higher chip rate
candidate proposal of 7.68Mchip/s discussed now by 3GPP. Thus, it
can be seen that, JD technique has become one of the key
technologies in current TDD CDMA systems.
[0004] T3G, a JV organized by Datang, Philips and Sumsang to
develop TD-SCDMA handset solution designs, has adopted JD
algorithms of ZF-BLE (ZF-BLE: zero forcing block linear equalizer)
and MMSE-BLE (minimum mean square error block linear equalizer) in
her first 3G mobile products.
[0005] However, the implementation of ZF-BLE and MMSE-BLE
algorithms needs to know as precondition the spreading codes of all
active UEs. For the base station, this won't pose as a problem,
because the base station is responsible for resource allocation and
thus can know the spreading codes of all users very easily. But for
a UE, it only knows its own spreading code and has no knowledge of
the spreading codes of other UEs sharing the same timeslot. Thus it
is no easy job to implement JD algorithms for UEs.
[0006] To implement JD algorithms in UEs, one solution is to add an
additional "active-code detection" module in the receiver of a
TD-SCDMA handset so that information about other UEs' spreading
codes can be recovered in a single UE, which can be referred to
"Performance of active codes detection algorithms for the downlink
of TD-SCDMA system," IEEE Inter. symposium on circuit and systems
(ISCS), Vol. 1, 2002, pp. 613-616, by Kang Shao-li et al, and
"Technology requirements of the 3GPP-TDD terminal," IEEE 2000
Inter. conf. on 3G Mobile communication technologies, pp. 89-93 by
S. Kourist et al. Unfortunately, this solution using "active-code
detection" module has very poor performance in some cases,
especially in the environment of lower vehicle speed and multipath
fading, which causes severe system capacity loss.
[0007] There is also another optional solution of adopting
equalized single user detection JD algorithm called MMSE-BLE-SD,
which can be referred to "Data detection algorithms specially
designed for the downlink of CDMA mobile radio systems," IEEE
International Conf. on Vehicle Technology (VTC), Vol. 1, May 1997,
pp. 203-207, by A. Klein. Compared with ZF-BLE/MMSE-BLE, the
performance of MMSE-BLE-SD is a little poorer, but its advantage is
only need to know the spreading code of the UE. However,
MMSE-BLE-SD algorithm also has to know the ACN (active code number)
allocated in the same timeslot as the UE in advance. Although the
ACN can be estimated at the UE by some special algorithms, the
single-user receiver's complexity and power consumption will be
increased heavily due to the added huge computation loads.
[0008] In fact, the above two problems can both be easily overcome
through sending the mandatory information of the spreading codes or
the ACN via some downlink channels to each UE by the base
station.
[0009] A method of transmitting the related spreading codes
information from the base station via common control channel (such
as BCH) to UEs, is described in the patent application document
entitled "Mobile station enabled for use of an advanced detection
algorithm", submitted on Jan. 13, 2003, filed by KONINKLIJKE
PHILIPS ELECTRONICS N.V. and EPO Application Serial No. 03075075.6.
According to the method as disclosed in this patent application,
the spreading code associated with a midamble can be obtained from
the midamble allocation information. However, it is restricted to
the case of knowing the association relationship between midambles
and channelization codes, that is, the so-called "default midamble"
case. There are two other midamble allocation cases in the 3GPP TDD
standard: (i) the "common midamble", wherein all users sharing the
same timeslot use the same midamble; (ii) the "midamble allocation
by signaling from higher layers", wherein there is no fixed
relationship between the allocated spreading codes and midambles,
which can be referred to 3GPP Technical Specifications 25.221,
"Physical Channels and mapping of transport channels onto physical
channels (TDD)", (Release 4), March, 2001. In these two cases, the
method as disclosed in the patent application has some
restricts.
[0010] A method to broadcast the CAI (codes allocation information)
directly on downlink common control channel (such as BCH) is
proposed in the patent application document entitled "Method and
apparatus for supporting P2P communication in TDD CDMA system",
filed by KONINKLIJKE PHILIPS ELECTRONICS. N.V. and the Application
Serial No. 03110415.0. According to the method as disclosed in this
patent application, common control channel has fixed position in a
radio frame or sub-frame (for instance, BCH is in TS0), thus every
UE can receive the CAI and perform JD by using the CAI. But, a
problem will arise when BCH is used to transfer the information.
The repetition period of BCH is at least 80 ms (8 radio frames) or
even longer (160, 320, or 640 ms, to be decided by the higher
layer).
[0011] When CAI varies rapidly, it's likely too late to update the
information. Moreover, if a large mount of CAI has to be
transmitted over BCH every repetition period, continuous overloads
on BCH will happen inevitably.
[0012] In fact, the change of CAI only occurs in three situations:
first, early when communication connection is being established,
the base station allocates spreading codes to new UEs; second,
during communication course, change of users in the same timeslot
occurs, for example, other users enter or leave the timeslot and
thus the allocation of spreading codes changes accordingly; third,
communicating UEs handover to other cells and release the spreading
codes in the former cell. It can be seen from the three cases that,
the change of CAI only occurs in certain time period. If the system
is very stable, it is of no necessity to transmit the CAI every
repetition period over BCH. Moreover, the change of CAI only
affects UEs associated with the same timeslot, but has no impact on
any other UEs working in other timeslots.
[0013] Therefore, a more effective method is needed to provide CAI
so that the UEs can perform JD algorithms by using the CAI.
SUMMARY OF THE INVENTION
[0014] The above analysis shows, when CAI changes in TDD CDMA
communication systems, it can be a more reasonable way to
retransmit the changed CAI in the associated downlink timeslot.
[0015] One object of the present invention is to provide a method
and apparatus for supporting downlink JD in TDD CDMA communication
systems. With the method and apparatus, CAI will only be sent to
the associated UEs when CAI changes so that each UE receiving the
CAI can implement ZF-BLE/MMSE-BLE JD algorithm by using the CAI,
thus the communication quality for each UE can be improved.
[0016] Another object of the present invention is to provide a
method and apparatus for supporting downlink JD in TDD CDMA
communication systems. With the method and apparatus, the ACN will
only be sent to the associated UEs when the ACN changes, so that
each UE receiving the ACN can implement ZF-BLE/MMSE-BLE JD
algorithm by using the ACN, thus the communication quality for each
UE can be improved.
[0017] A method is proposed in this invention for supporting
downlink JD (joint detection), to be performed by a TDD CDMA
communication network system, comprising: (a) judging whether the
CAI (codes allocation information) for a downlink timeslot will
change in the next TTI (transmission time interval); (b) inserting
the changed CAI as a specific control information into a specified
field in the traffic burst in the downlink timeslot corresponding
to current TTI if the CAI will change; (c) sending the traffic
burst containing the specific control information to each UE in the
downlink timeslot via a downlink channel. Wherein the initial CAI
is sent to the UE by the network system when the network system
establishes connection with the UE.
[0018] A method is proposed in this invention for supporting
downlink JD, to be performed by a UE in a TDD CDMA communication
system, comprising steps of: (i) in the downlink timeslot,
receiving a traffic burst transferred by the network system via the
downlink channel; (ii) detecting whether the traffic burst contains
the CAI in the next TTI for the downlink timeslot; (iii) extracting
the CAI if the traffic burst contains the CAI; (iv) performing
next-phase JD algorithm to decrease interference by using the
CAI.
[0019] A method is proposed for supporting downlink single-user JD
in a TDD CDMA communication system, to be performed by a network
system, comprising steps of: (a) judging whether the ACN for a
downlink timeslot will change in the next TTI; (b) inserting the
changed ACN as a specific control information into a specified
field in the traffic burst in downlink timeslot corresponding to
current TTI if the ACN will change; (c) sending the traffic burst
containing the specific control information to each UE in the
downlink timeslot via downlink channel. Wherein the network system
sends the initial ACN to the UE when the network system establishes
connection with the UE.
[0020] A method is proposed for supporting downlink single-user JD
in a TDD CDMA communication system, to be performed by a UE,
comprising steps of: (i) receiving a traffic burst transferred by
the network system via downlink channel in a downlink timeslot;
(ii) detecting whether the traffic burst contains the ACN for the
downlink timeslot in the next TTI; (iii) extracting the ACN if the
traffic burst contains the ACN; (iv) performing the next-phase
single-user JD algorithm by using the CAN, to decrease
interference.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] For a detailed description of the preferred embodiments of
the invention, reference will now be made to the accompanying
drawings in which:
[0022] FIG. 1 illustrates the sub-frame and timeslot structures
used in conventional TD-SCDMA systems;
[0023] FIG. 2 illustrates the sub-frame and timeslot structures
with UE specific control symbols in conventional TD-SCDMA
systems;
[0024] FIG. 3 illustrates the downlink timeslot formats in
conventional TD-SCDMA systems;
[0025] FIG. 4 illustrates structure of the revised traffic burst
including CAI/ACN information in TD-SCDMA system in accordance with
the present invention;
[0026] FIG. 5 illustrates the mapping relationship of the CAI in
TD-SCDMA system in accordance with the present invention;
[0027] FIG. 6 illustrates the downlink timeslot formats after the
CAI is inserted in TD-SCDMA system in accordance with the present
invention;
[0028] FIG. 7 illustrates the ACN represented by the ACN
information in TD-SCDMA system in accordance with the present
invention;
[0029] FIG. 8 illustrates the downlink timeslot formats after the
ACN information is inserted in TD-SCDMA system in accordance with
the present invention;
[0030] FIG. 9 is a block diagram illustrating the hardware modules
implementing the method for supporting downlink JD in TDD CDMA
communication system in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] In the following, TD-SCDMA system will be exemplified to
describe the present invention in conjunction with accompanying
figures. Referring to the technical scheme of the present
invention, when the above CAI/ACN information changes, the base
station inserts the changed CAI/ACN information into the traffic
burst to be transmitted, and sends the traffic burst in downlink
timeslot to each UE in the downlink timeslot via DPCH (dedicated
physical channel). Each UE executes next-phase ZF-BLE/MMSE-BLE or
MMSE-BLE-SD JD algorithms according to the detected CAI.
[0032] The above scheme of the present invention, especially the
detailed procedure as how the base station inserts the changed
CAI/ACN information into the traffic burst to be transmitted, can
be more fully understood with reference to FIG. 1 to FIG. 3,
wherein a brief introduction will first be given to the sub-frame
and traffic burst (i.e. timeslot) structures used in TD-SCDMA
system in 3GPP standards.
[0033] In TD-SCDMA system, a radio frame is 10 ms in duration, and
every radio frame is divided into two sub-frames, wherein each
sub-frame is 5 ms in duration and composed of 6400 chips. As FIG. 1
shows, every sub-frame is composed of 7 traffic timeslots TS0-TS6
and 3 special pilot timeslots, wherein every traffic timeslot is
composed of 864 chips, TS0 is always used for carrying downlink
data, TS1 is always used for carrying uplink data, and TS2-TS6 can
be used for respectively carrying data in uplink or downlink. As to
the three special pilot timeslots, DwPTS is downlink pilot timeslot
(96 chips), UpPTS is uplink pilot timeslot (160 chips) and GP is
guard period (96 chips). Every traffic timeslot is divided into 4
fields, including data field 1 (352 chips), midamble field (144
chips), data field 2 (352 chips) and the empty field GP for
timeslot guard (16 chips), wherein besides the traffic data symbols
carried in two data fields 1 and 2, there can also be some UE
specific control symbols, such as TPC (Transmitter Power Control),
SS (Synchronization Shift) and TFCI (Transmitter Format Combination
Indicator). The base station can provide some control information
to each UE by using these UE specific control symbols.
[0034] FIG. 2 illustrates the sub-frame and timeslot structures
loaded with UE specific control symbols. UE specific control
symbols are located at two sides of midamble (or namely pilot
symbol), and the control symbols for SS and TPC respectively occupy
the places of some data symbols in data field 2 in one timeslot of
each sub-frame. Whereas the control symbols for TFCI are divided
into four parts, the first and second parts respectively occupy the
places of some data symbols in data field 1 and data field 2 in one
timeslot (the same as SS and TPC) of a sub-frame in a radio frame,
and the third and fourth parts respectively occupy the places of
some data symbols in data field 1 and data field 2 in the
corresponding timeslot of another sub-frame in the radio frame. The
control symbols for TPC, SS and TFCI are located in the data field
in traffic timeslot, so they can be sent to each UE only after
being coded and spread, just as other data symbols. After receiving
the data containing the above control information from the base
station, each UE has to recover the information contained in these
control symbols through some basic baseband processing.
[0035] A brief description is given above to the frame and timeslot
structures in TD-SCDMA system. In a timeslot, the structure of
traffic burst or namely the allocation of traffic data and UE
specific control symbols, depends on many aspects, such as the
timeslot is used for uplink or downlink, the spreading factor and
so on. For example, according to the standard of conventional
TD-SCDMA protocols, the uplink spreading factor (SF) can be 1, 2,
4, 8 or 16, while the downlink SF can only be 1 or 16. According to
the relationship between the number of the data symbols
accommodated in the data field and the SF as promulgated in the
protocols, S.times.SF=352 chips, an uplink timeslot can accommodate
704, 352, 176, 88 or 44 data symbols (two data fields are included
in a timeslot). According to QPSK modulation which puts two bits in
a symbol, an uplink timeslot can have 1408, 704, 352, 176 or 88
bits corresponding to different SFs. On the other hand,
corresponding to the fact that the downlink SF can be 1 or 16, a
downlink timeslot can contain 704 or 44 data symbols. According to
QPSK modulation which puts two bits in a symbol, a downlink
timeslot can have 1408 bits when SF=1, and 88 bits when SF=16.
[0036] FIG. 3 illustrates the downlink timeslot formats in
conventional TD-SCDMA systems, wherein the number of bits NTFCI in
the fourth column for coded control symbols TFCI can be 0, 4, 8, 16
or 32 bits respectively (these bits will be allocated evenly to a
radio frame or namely two sub-frame) according to the amount of
TFCI information. As to control symbols SS and TPC in the fifth
column, when SF=16, if information about SS and TPF is not included
in the timeslot, the number of bits for SS and that for TPC are
both 0, and if information about SS and TPF is included in the
timeslot, the number of bits for SS and that for TPC are both 2.
Similarly, when SF=1, the number of bits NSS for SS and the number
of bits NTPC for TPC can both be 1, 2 or 32.
[0037] As FIG. 3 illustrates the example of the timeslot format
whose sequence is 8, when SF=16, the number of bits included in the
downlink timeslot is 88 as noted above.
[0038] In the downlink timeslot, NTFCI in the fourth column is 16
bits. According to the protocol, these 16 bits can be divided into
4 parts, the 4 bits of the first or third part occupy 4 bits in
data field 1 of the timeslot, while the 4 bits of the second or
fourth part occupy 4 bits in data field 2 of the timeslot. NSS and
NTPC in the fifth column are both 2 bits, occupying 2 bits in data
field 2 of the timeslot respectively. NTFCI, NSS and NTPC all need
to use data field for transfer, so there are 76 bits remained
(88-8(NTFCI)-2(NSS)-2(NTPC)=76) of the 88 bits of the timeslot for
data transfer service, wherein the 44-bit data field 1 has 40 bits
remained (44-4(NTFCI of the first or third part)=40) for data
transfer service, and the 44-bit data field 2 has 36 bits remained
(44-4(NTFCI of the second or fourth part)-2(NSS)-2(NTPC)=36) for
data transfer service. After the UE specific control symbols are
inserted, the number of bits for data transfer in the timeslot, in
data field 1 and 2 of the timeslot can respectively be represented
by Ndata/Slot, Ndata/field(1) and Ndata/field(2) in the seventh,
eighth and ninth column as shown in FIG. 3.
[0039] The proposed method for UEs to perform JD by using dedicated
physical channel to transfer the changed CAI or ACN when the CAI or
ACN changes, is similar to the above method of inserting UE
specific control symbols TFCI, SS and TPC into the data field of
the traffic timeslot. In the present invention, control symbols for
the changed CAI or ACN are inserted into data field 1 or 2 of the
traffic timeslot, and then sent to UEs via downlink channel after
being coded and spread.
[0040] FIG. 4 illustrates structure of the revised traffic burst
including CAI/ACN information in TD-SCDMA system in accordance with
the present invention, wherein control symbols for CAI/ACN occupy
some places of data symbols in data field 1, which is preceding
TFCI of the first or third part (CAI/ACN can also be allocated
behind TFCI in data field 2, or in other places in data field
1).
[0041] In the following, a description will be given to the
detailed procedures of inserting CAI and ACN information
respectively into data field of the traffic timeslot when adopting
ZF-BLE/MMSE-BLE and MMSE-BLE-SD algorithms to implement JD, based
on the timeslot structure as shown in FIG. 4, in conjunction with
FIG. 5 to FIG. 8.
I. Implementing Downlink JD with ZF-BLE or MMSE-BLE
[0042] As described above, in the downlink of TD-SCDMA system, SF
can only be 1 or 16. When SF is 1, only one user is allocated in
the timeslot. There is no spreading at all in this case, so no
problem exists for the allocation of spreading codes. Hence, this
invention only takes the case where SF is 16 into
consideration.
[0043] When SF=16, at most 16 spreading codes in a timeslot can be
assigned to 16 code channels, so a timeslot can use 16 bits (two
bytes) to represent allocation of 16 spreading codes. Referring to
the mapping of CAI as displayed in FIG. 5, Bit15 to Bit0
respectively corresponds to the spreading codes Code15 to Code0
used by the 16 code channels, wherein if Bit i=1, the corresponding
spreading code Codei is used by a user in the timeslot, and if Bit
i=0, the corresponding spreading code Codei is not allocated to any
UE yet. For example, when Bit0 and Bit5 are 1 while other bits are
all 0 in FIG. 5, it means that only the corresponding spreading
codes Code0 and Code5 are used by UEs while other spreading codes
are not allocated yet.
[0044] In downlink traffic timeslot, when the 16-bit CAI (the
actual bit information may change after being channel coded, so we
just assume that the transferred information is the 16-bit original
bit information) shown in FIG. 5 is transferred using the data
field, the traffic timeslot format as shown in FIG. 3 will change
correspondingly, and the revised format is illustrated in FIG. 6.
For convenience of comparison, the timeslot format sequences in the
first column in FIG. 6 can respectively be denoted as n and n',
wherein the row corresponding to n shows the timeslot format before
CAI is inserted, and the row corresponding to n' shows the timeslot
format after CAI is inserted, which are marked respectively in
light and dark shadow. In any case, the timeslot formats denoted by
n and n' will not occur concurrently.
[0045] Compared with FIG. 3, NCAI is added in the fourth column of
FIG. 6, for representing CAI. When NCAI=0, it means that CAI has
not changed and thus need not be transferred; when NCAI=16, it
means that CAI changes, for example, when one or more active UEs
leave the downlink timeslot and the base station needs to reclaim
the spreading code resource released by the UEs, or when one or
more UEs join the downlink timeslot and the base station needs to
allocate spreading code resource for new UEs, or when the base
station needs to reallocate the spreading code resource in the
downlink timeslot to optimize resource configuration in the
downlink timeslot, thus the 16-bit CAI needs to be transferred to
indicate the current utilization of each spreading code in FIG. 5
corresponding to the CAI. After the CAI is inserted, the number of
bits for data transfer, in data field 1 and 2 of the downlink
timeslot can respectively be represented by Ndata/Slot,
Ndata/field(1) and Ndata/field(2) in the eighth, ninth and tenth
column as shown in FIG. 6.
[0046] When the base station judges that the CAI in a downlink
timeslot will change in the next TTI, it will insert the changed
16-bit CAI as a specific control information into the data field
(like the first data field as shown in FIG. 4) of the traffic burst
corresponding to the downlink timeslot in current TTI, and spread
the CAI along with other traffic data, UE specific control symbols
TFCI, SS and TPC (if they exist). Then, the spread traffic burst
containing the specific control information will be sent to each UE
in the downlink timeslot, via downlink channel such as DPCH.
[0047] When a UE in the downlink timeslot receives the traffic
burst from the base station via the DPCH, it first detects whether
CAI is included in the traffic burst, just like detecting UE
specific control symbols TFCI, SS and TPC. If CAI is included, it
will be extracted and the UE can learn the allocation and
utilization of the spreading codes in FIG. 5 corresponding to the
CAI. Then, the UE makes preparation for implementing JD algorithms
in the next TTI, by taking advantage of the detected CAI, that is
to say, the extracted CAI is the CAI for the downlink in the next
TTI. If CAI is not included in the traffic burst received by the
UE, it indicates that the CAI has not changed, and the UE can
execute next-phase JD algorithm according to prior CAI.
[0048] It should be noted herein: same as other traffic data, the
CAI inserted into the data field need be spread before being
transmitted, so user terminals have to use advanced receiving
algorithms (such as JD) to detect the CAI effectively after
receiving the information. But implementation of JD algorithms need
know the information about the spreading codes in the timeslot in
advance, hence the proposed method can't be used to despread and
decode the data from the downlink by using the CAI in current
timeslot. Therefore, the CAI detected in the above steps of the
present invention, can only be used by the UE to executed JD
algorithm in the next TTI (a TTI may include several sub-frames and
is an interleaving period during which CAI won't change). When the
UE establishes communication connection with the base station, the
base station sends the initial CAI to the UE over BCH or other DCHs
in an initializing fashion, so that the UE can execute JD
algorithms by using the initialized CAI when receiving subsequent
traffic burst transferred in the downlink timeslot, to detect
whether new changed CAI has been sent to the UE.
[0049] Because the base station manipulates allocation of radio
resources, at the beginning of establishing communication
connection with the UE, the base station announces the initial CAI
to the UEs allocated in the downlink timeslot, and in current TTI
inserts the forecasted changed CAI in the next TTI into the
downlink timeslot of current TTI to transfer it to each UE in the
downlink timeslot. This shouldn't be a hard job for the base
station in communication techniques.
[0050] As described above, the UE can detect that the network
system dispatches the changed CAI via downlink when the CAI
changed, thus can execute ZF-BLE/MMSE-BLE algorithm by using the
received CAI.
II. Implementing Downlink JD with MMSE-BLE-SD
[0051] Different from implementing JD by using ZF-BLE/MMSE-BLE
algorithm, when MMSE-BLE-SD is adopted, the UE only need know the
ACN K in current timeslot without knowledge of the detailed CAI in
the timeslot. Based on this, we can use 4 bits to represent the 16
possibilities of the ACN in the timeslot, as shown in FIG. 7.
[0052] When the 4-bit ACN (the actual bit information may change
after being channel coded, and we assume that the 4 bit original
bit information is transferred) in FIG. 7 is sent in the downlink
timeslot by using the data field, the traffic timeslot format shown
in FIG. 3 has to be altered accordingly, and the revised format is
illustrated in FIG. 8. For ease of comparison, the timeslot format
sequences in the first column in FIG. 8 are also denoted as n and
n' respectively, wherein the row corresponding to sequence n shows
the timeslot format when ACN is not inserted, while the row
corresponding to sequence n' shows the timeslot format after ACN is
inserted, and they are marked respectively in light and dark
shadows, moreover the timeslot format denoted by n and that by n'
will not occur concurrently in any case.
[0053] Compared with FIG. 3, the fourth column NAC is added into
FIG. 8, for denoting the ACN in current timeslot. When NAC=0, it
means that the ACN in current timeslot has not changed and it's no
necessity to send the ACN information; when NAC=4, it means that
the ACN in current timeslot has changed and it's necessary to send
the 4-bit ACN information. The number of bits for transferring
traffic data in the downlink timeslot, in data field 1 and data
field 2 in the downlink timeslot after the ACN information is
inserted, can respectively be denoted as Ndata/Slot, Ndata/field(1)
and Ndata/field(2) in the eighth, ninth and tenth column in FIG.
8.
[0054] When the base station judges that the ACN in a downlink
timeslot will change in the next TTI, the 4-bit changed ACN
information is inserted as a specific control information into the
data field of the traffic burst in the downlink timeslot
corresponding to the downlink timeslot in current TTI, such as the
data field 1 as shown in FIG. 4. Then, the ACN information will be
coded and spread along with other traffic data, and UE specific
control symbols TFCI, SS and TPC (if UE specific control symbols
exist). Afterwards, The coded, spread traffic burst containing the
specific control information is sent to each UE in the downlink
timeslot via the downlink channel, such as DPCH.
[0055] When receiving the traffic burst via the DPCH from the base
station, a UE in the downlink timeslot first detects whether ACN
information is contained in the traffic burst, just like the method
of detecting UE specific control symbols TFCI, SS and TPC. If ACN
information is contained, the ACN will be extracted, and the UE
will make preparations for executing single-user JD algorithm in
the next TTI, that is, the extracted ACN information is the ACN of
the downlink timeslot in the next TTI. If ACN information is not
contained in the traffic burst received by the UE, it shows that
the ACN has not changed, and the UE can execute single-user JD
algorithm of the subsequent phase, according to prior ACN.
[0056] Just like adopting ZF-BLE/MMSE-BLE algorithm as above, the
ACN information detected in the steps of detecting ACN information,
can only be provided to the UE for use in executing single-user JD
algorithm in the next TTI. The initial ACN information can be
provided to the UE by the base station in an initializing manner
early when the UE establishes communication connection with the
base station.
[0057] As described above, because the UE detects that the network
system sends the changed ACN information via downlink when the ACN
information changes, the UE can execute MMSE-BLE-SD algorithm by
using the received ACN information.
[0058] In accordance with the foregoing method, during
communication procedure, when the CAI or ACN information changes,
the base station can insert the changed CAI or ACN information into
corresponding traffic burst in form of specific control
information, so that the UE receiving the traffic burst can execute
JD algorithm according to the CAI or ACN information, and thus
decrease interference during communication procedure. For UEs not
in communication procedure, for example, when a UE is establishing
communication connection or the communication connection is being
handed over to other cells, the initialized CAI or ACN information
can be sent to the UEs as a portion of resource allocation message
or handover command message, so that the UEs can execute JD
algorithm according to the CAI or ACN information in the resource
allocation message or handover command message, and thus reduce
interference during call establishment and cell handover
procedures.
[0059] The proposed method above is applicable to not only low
chip-rate TD-SCDMA system, but also high chip-rate system with 3.84
chips/s and higher chip-rate system with 7.68 chips/s.
[0060] The method for inserting the CAI or ACN information into the
traffic burst in form of specific control information and the
method for detecting and utilizing the CAI or ACN information as
proposed in the present invention, can be implemented as computer
software, or hardware modules with the software functions, or
combination of both.
[0061] When the proposed downlink JD method is implemented as
hardware modules, the network system and the UE can be illustrated
in FIG. 9, wherein the components same as those in current network
systems and UEs are not given herein.
[0062] When an active UE leaves a downlink timeslot, or a new UE
joins a downlink timeslot, or the network system reallocates the
spreading code resource in a downlink timeslot, judging unit 101 in
network system 100 judges whether the CAI will change in the next
TTI. Inserting unit 102 inserts the changed CAI as specific control
information into a specified field in the traffic burst in the
downlink timeslot corresponding to the downlink timeslot in current
TTI. Then, transmitting unit 103 sends the traffic burst containing
the specific control information to each UE in the downlink
timeslot via a downlink channel. Wherein the initial CAI is sent to
each UE through transmitting unit 103 when the network system is
establishing connection with the UE.
[0063] Receiving unit 201 in UE 200 receives the traffic burst sent
by the network system via the downlink channel in a downlink
timeslot. Detecting unit 202 detects whether the traffic burst
contains CAI of the downlink timeslot in the next TTI. If CAI is
contained, extracting unit 203 will extract it from the traffic
burst, and provides it to executing unit 204 for executing
next-phase ZF-BLE/MMSE-BLE JD algorithm. Wherein the initial CAI is
received from the network system when receiving unit 201 is
establishing connection with the network system.
[0064] When an active UE leaves a downlink timeslot, or a new UE
joins a downlink timeslot, judging unit 101 in network system 100
judges that the ACN in the downlink timeslot will change in the
next TTI. Inserting unit 102 inserting the ACN as a specific
control message into a specified field of the traffic burst in the
downlink timeslot corresponding to the downlink timeslot in current
TTI. Then, transmitting unit 103 sends the traffic burst containing
the specific control information to each UE in the downlink
timeslot via downlink channel. Herein, the initial ACN is sent to
the UE by transmitting unit 103 when the network system is
establishing connection with the UE.
[0065] Receiving unit 201 in UE 200 receives the traffic burst in a
downlink timeslot sent by the network system via the downlink
channel. Detecting unit 202 detects whether the traffic burst
contains the ACN of the downlink timeslot in the next TTI. If the
ACN is contained, extracting unit 203 extracts the ACN from the
traffic burst, and provides it to executing unit 204 for executing
next-phase MMSE-BLE-SD JD algorithm. Herein, receiving unit 201
receives the initial ACN from the network system when establishing
connection with the network system.
Beneficial Results of the Invention
[0066] Regarding to the above description of the embodiment of the
present invention in connection with accompanying figures, in the
proposed method and apparatus for supporting downlink JD in TDD
CDMA communication systems, only when the CAI/ACN information in a
timeslot changes, the base station will insert the changed CAI/ACN
information in form of specific control information into the
traffic burst and send the traffic burst to each UE in the downlink
timeslot via DPCH, which avoids the overload phenomenon on BCH
likely caused by sending CAI/ACN information every BCH repetition
period, and avoids the unnecessary computation and power
consumption brought by the fact that UEs in other timeslots also
read the CAI/ACN information when the CAI/ACN information is sent
via common control channels.
[0067] Meanwhile, with regard to the proposed method and apparatus
for supporting downlink JD in TDD CDMA communication systems, a UE
can execute ZF-BLE/MMSE-BLE or MMSE-BLE-SD algorithm according to
the CAI/ACN information contained in the received traffic burst,
thus to mitigate interferences during communication procedure and
improve communication quality for the UE.
[0068] Furthermore, with regard to the proposed method and
apparatus for supporting downlink JD in TDD CDMA communication
systems, spreading codes are not transferred with the help of
midamble information, so it is not subject to the constraint of the
fixed relationship between midamble and spreading codes, and thus
is applicable to various midamble allocation schemes in 3GPP
standards.
[0069] The previous description of the disclosed embodiments is
provided to enable any person skilled in the art to make or use the
present invention. Various modifications to these embodiments will
be readily apparent to those skilled in the art, and the generic
principles defined herein may be applied to other embodiments
without departing from the spirit or scope of the invention. Thus,
the present invention is not intended to be limited to the
embodiments shown herein but is to be accorded the widest scope
consistent with the principles and novel features disclosed
herein.
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